EarthFort.com is the marketing arm of Dr. Ingham's SFI organization. Here's a blurb
on the differences between fish emulsion vs. fish hydrolysate from their web site store.
Fish hydrolysate is cold processed (minced, enzymatically digested and liquefied) to preserve proteins for quick turnover by microbes into nutrients for plants. This process distinguishes fish hydrolysate from fish emulsion which is processed with heat; removing oils (fungal foods) and denaturing nutrients and beneficial bacteria. Hydrolysate retains the natural oils from the fish that are a very potent fungal food.
Because of cold processing, fish hydrolysate must be stabilized at a low pH. We recommend hydrolysates that are stabilized with sulfuric or phosphoric acid.
Some nationally distributed sources of fish hydrolysate would be Neptune's Harvest, Organic Gem & others. There are however a number of regional hydrolysate products.
You can also make your own - it ain't rocket science